An experimental investigation of Reactivity Controlled
Compression Ignition (RCCI) combustion was conducted in a small
single-cylinder HSDI diesel generator engine and compared to
standard Direct Injection (DI) diesel combustion to assess the
validity of this combustion strategy for high efficiency operation
and simultaneous NOx and soot emission reduction in cylinder for
this type of engine. A Yanmar L70AE engine was modified from its
unit injector mechanical fuel system to operate with a more
flexible, electrically controlled common rail DI fuel system in
order to achieve the high level of injection event control required
for RCCI combustion.
RCCI combustion was realized using split, early DI diesel fuel
and Port Fuel Injected (PFI) gasoline for 25%, 50% and 75% engine
loads (~3, 4.3 and 5.5 bar IMEPn). The effects of intake air
temperature, DI injection timing and combustion phasing on engine
efficiency, emissions and combustion stability were explored.
The results indicated that RCCI combustion was effective at
reducing NOx and soot emissions, but suffered from increased HC and
CO emissions, and poor combustion efficiency at light loads, and
higher levels of combustion variation compared to conventional
diesel combustion. Thermal efficiency of RCCI combustion suffered
at low loads due to poor combustion efficiency. At 75% load, RCCI
attained nearly a 3% efficiency improvement over standard diesel
combustion, indicating that there is significant opportunity to
reduce light load fuel consumption with further optimization effort
focused on combustion efficiency.